Oxidative dehydrogenation (ODH) of light alkanes catalyzed by metal oxides is considered to be a thermodynamically favorable process for olefin production. The strong interaction between the unoccupied d-orbital of metal atom and the π-electrons of olefins, however, leads to deep oxidation of olefin to CO2, especially at elevated temperatures. The challenge lies in the development of selective and low-temperature active catalysts to avoid such unwanted deep oxidation. Here, we report unambiguous evidence on properly prepared mesoporous silica-supported boron oxide catalysts showing high selectivity for ODH of propane. The catalysts are active at a temperature as low as 405 °C, showing a propane conversion of 2.8% and a propene selectivity of 84.1% (C2–3 =: 94.6%). Upon raising the temperature to 450 °C, a propane conversion of 14.8% can be achieved, with a selectivity of 73.3% toward propene or 87.4% for both propene and ethene (C2–3 =). Both experimental and theoretical studies indicate tricoordinated boroxol and hydroxylated linear boron species are the active sites for the ODH of propane. In addition, the oxophilicity of boron sites is responsible for suppressing deep oxidation by eliminating the alkoxyl species, leading to high selectivity toward olefin products.

Metal-free boron- and carbon-based catalysts for the oxidative dehydrogenation of light alkanes is reviewed from the preparation methods, characterization, catalytic performance and mechanistic issues.

Metal-free boron-based catalytic systems are growing to be promising choices in the oxidative dehydrogenation (ODH) of light alkanes to olefins. However, the ambiguity in the understanding of the mechanism has impeded the improvement of novel catalytic systems. Herein, by using density functional theory (DFT), we mapped a complex reaction network for the B 2 O 3catalyzed ODH of propane, which displayed a typical feature of interplay between the on-surface and off-surface channels through the whole reaction from the initiation stage to the termination stage. The results showed that the interplay between the channels in the two regimes was necessary in two aspects: On one hand, to guarantee high selectivity for olefin products, the gaseous channels need the intervention of the surface sites to eliminate the oxygenated intermediates, for example, alkoxyl radicals, that would otherwise evolve into deep oxidation products. On the other hand, to maintain the high conversion of propane, the catalyst surface needs gaseous radicals to regenerate reactive >BO• species. The mechanism also well explained the catalytic role of trace water and addressed the surface dynamical restructuring, thus constituting a plausible comprehensive understanding of the ODH of propane catalyzed by an oxygenated boron system.